Reflexive Airway Sensorimotor Responses in Individuals with Amyotrophic Lateral Sclerosis

Progressive motor denervation in amyotrophic lateral sclerosis (ALS) leads to reduced expiratory cough flow and diminished airway clearance physiologic capacity. Although ALS is thought to primarily impact motor systems, preliminary data from our laboratory suggest degradation of afferent pathways that regulate reflexive cough responses to radiographically confirmed aspiration. We, therefore, aimed to delineate both sensory and motor responses to a tussigenic airway irritant in individuals with ALS compared to healthy controls.

Thirty-two individuals with ALS and 34 healthy age and gender-matched controls completed reflex cough testing. Capsaicin stimuli (0, 50, 100, 150, 200 μM) were presented in a randomized three-block design and motor (cough spirometry metrics) and sensory (patient-rated urge to cough, UtC) ratings collected. ALS patients underwent videofluoroscopy with penetration-aspiration ratings completed. Descriptives, Mann-Whitney U, and mixed models ANOVAs were performed.

Sensory: Individuals with ALS demonstrated greater UtC sensitivity slopes (i.e., increased stimulus sensitivity) vs. healthy controls (p = 0.036). Within the ALS group, however, silent aspirators (PAS = 8) demonstrated blunted UtC sensitivity slopes compared to ALS patients who did not (PAS ≤ 7, p = 0.0001). Motor: Compared to healthy controls, ALS individuals demonstrated reduced peak expiratory flow rates (p = 0.004), longer peak expiratory rise time (p = 0.017), and lower cough volume acceleration (p = 0.000).

ALS individuals demonstrated increased sensitivity to an upper airway irritant; however, they demonstrated slower and weaker expiratory cough motor output compared to healthy controls. In ALS silent aspirators, blunted sensorimotor responses were observed, suggesting that sensory degradation may occur at the final or most severe stage of bulbar disease progression.